1. Field of the Invention
The present invention relates to composites manufacturing. In particular, the present invention relates to a mandrel extraction tool and a method of using same.
2. Description of Related Art
Structural components of modern aircraft are often constructed of composite materials. These materials typically include a fabric, mat, or other plurality of fibers disposed in a rigid, polymeric matrix. As shown in FIG. 1, such a structural component 101 includes one or more stiffeners or stringers 103 adhesively bonded to an inner surface or “inner mold line” 105 of a skin 107. Stringers 103 provide stiffness and strength to structural component 101 even with a relatively thin skin 107.
In the particular example of FIG. 1, stringer 103 is often referred to as a “T” or “I” stringer, relating to the cross-sectional shape of stringer 103. Stringer 103 is typically fabricated by applying “C” shaped portions 109 of uncured composite material around each of two mandrels 111, and then abutting the two portions of composite material, generally at 113. Radius filler material is typically applied to voids between upper and lower radii of the abutted portions of composite material. One or more additional layers of uncured composite material are often applied to a top 115 and bottom 117 of stringer 103, across interface 113 between the two portions of abutted composite material. Uncured stringer 103 is then heated, under pressure in an autoclave, under vacuum in a vacuum bag, or both, to cure the polymeric matrix and form a rigid, cured stringer 103. Stringer 103 may be cured concurrently with skin 107 or separately from skin 107.
Typically, the polymeric matrix of the composite material comprising stringer 103 will become less viscous and will flow during the curing process. As illustrated in FIG. 2, it is common for some of the polymeric matrix to escape from stringer 103 and flow onto mandrel 111, forming a flash 201. The polymeric matrix becomes rigid during the curing process, either via cross-linking of thermosetting polymeric molecules or upon cooling of stringer 103, if the polymeric matrix comprising stringer 103 is a thermoplastic polymeric material. In either case, flash 201 can mechanically block removal of mandrels 111 from stringer 103.
Many procedures have been developed to address the problem of mandrel 111 removal. For example, a grinding or abrading process may be used to remove flash 201, thus allowing mandrel 111 to be removed from stringer 103. Such grinding or abrading processes, however, may inadvertently damage mandrel 111 and/or stringer 103, requiring repair to the damaged mandrel 111 and/or stringer 103. Wedges have been used to pry stringer 103 away from mandrel 111 and, thus, break flash 201. The forces applied to stringer 103 by such wedging processes, however, may inadvertently break the polymeric matrix and/or the reinforcing fibers of stringer 103, compromising the structural integrity of stringer 103.
Moreover, tools have been developed to mechanically urge mandrels 111 from stringer 103. These tools, however, rotate mandrels 111 from stringer 103, as indicated by arrows 119 in FIG. 1. By rotating mandrel 111 during extraction, forces applied to stringer 103 may inadvertently break the polymeric matrix and/or the reinforcing fibers of stringer 103, thus compromising the structural integrity of stringer 103.
While many procedures are known in the art for removing mandrels from cured composite structures, considerable room for improvement remains.